So, I read a (frustratingly short) newspaper article in a paper around here about Chinese engineering projects for "ocean cities" as a way of alleviating the pressure on land. As I was trying to figure out what it would look like, it was plain that the guy writing had got it mixed up. Was he thinking of cities built on the seafloor (as with Captain Nemo or some "mad professor" comic books), cities mined into the seafloor - or rafted cities floating/pyloned up on the sea surface? The examples of technical solutions and building ideas cited pointed in all different directions - at one point talking of huge funnels or shafts up through the water that would allow for ventilation and light (seems to imply a seabed city), gardens set at the bottom of that same kind of open shafts (ditto, but is a walled-off space let's say 150 m/425 feet square and 50 m deep , plus 20 m high walls above water to safeguard it against waves, suspended into the sea, and repeated many times over, really realistic today?) but elsewhere "floating residential qurters" and marinas. It was clearly a rewrite from some foreign paper, in English or Chinese, but not a good one, and googling around for this stuff is getting me nowhere.

The idea of those kinds of urban environments is really interesting of course (very visual and with lots of technical and human challenges) and in the past there's been some serious sketching-out of such projects, in the Netherlands for example. It looks likely to me that we'll get to see below-seafloor mining operations in the near future - mining for copper, gold and rare earth metals on the shelf or in the oceanic ridges - and that could lead to some kinds of closed-off underwater compounds too. Building an actual city for ordinary people on the seafloor or stretching on the sea surface, or on artificial islands, is a whole different proposition though.

Anyone else heard of these Chinese projects or sketches, or of similar city projects? What do you think and how would they overcome the challenges such as taking on sewage and freshwater, inflow of air and lighting, the flow of food, commodities, fuel and transportation coming in (imagine a city the size of Manhattan or Hamburg in around 1900 built as a sea project on a few artificial islands or platforms and the difficulties are clear...) or the safeguards against people actually falling into the sea?

There are various Libertarian 'floating commune' projects running around on the net. They're mostly focused on trying to build something that can last out in International waters indefinitely. So far I'm not aware of any successful designs, but that was a few years ago.

In theory, designing a self-sustaining sea-city isn't too different from designing a self-sustaining space station. Pressure differentials and oxygen balances would have to be factored in with an underwater setup, just as they are with an orbital platform, although the direction of the differential is reversed. It would be interesting if a few NASA vets were to get involved with one of these.

There are various Libertarian 'floating commune' projects running around on the net. They're mostly focused on trying to build something that can last out in International waters indefinitely. So far I'm not aware of any successful designs, but that was a few years ago.

There were a couple of attempts in the 1950's-70's, none of which met with any great success... two were reclaimed by governments and one sank almost immediately. There was another upsurge in interest during the mid-2000's but nothing really seemed to get beyond the planning stage.

Probably the closest thing to actually being a functional floating city is less a floating city and more a permanently moving cruise ship; MS The World. In essence it's basically a moving tax haven... because the ship spends so little time in any one country with a little tax work the residents who live on it nearly year round can effectively avoid paying the vast majority of taxes.

Yeah, there were some attempts back in the seventies to occupy a few abandoned islands in the straits off Copenhagen, near the border between Denmark and Sweden (but in Danish territorial waters alright). Those islets had decommissioned artillery forts but otherwise there wasn't much space for anything, and I think the settlem,ents ended fairly soon. The free city of Christiania, in an abandoned quarter of army barracks near downtown Copenhagen, was much moreof a success story, sort of - and a haven of controversy (not least about the street called, tellingly, "Pusher Street" where you could, for many years, openly buy any dope you wanted). That one still exists today, more than forty years after the initial squatting, despite many pledges by Danish politicians to oust the folks living there.

It's not every day I get to talk about my speciality - cities - so I'm happy to jump at the chance. Unfortunately, I've never encountered any 'serious' proposals for cities in the sea.

I see some problems right away, though. Maybe these are addressed, but I'd like to bring them up anyway. Because cities are more than just a collection of houses, and they have a more or less distinct set of requirements and problems, both of which would be difficult to meet at sea. Not impossible, mind you, but difficult.

Of the problems I can see, most or all are problems of scale. On a small scale, this approach could be quite sustainable. On a large scale, however, it would require some radical innovations. Getting supplies to the city ( cities - at least the overwhelming majority of them - are net consumers, and require surplus production elsewhere ). You might be able to get over this problem with farming, or production of edible algae, and obviously fishing. However, this would be quite intensive on space, and would require even more potable water than what you'd need for people to survive. This is mentioned on a seasteading site I found, but it gives no exact figures for how much space would be needed. It does mention that soil would have to be imported, however. I don't know enough about farming to tell you whether or not you could then survive on the imported soil alone ( through fertilization and so on ), or if you might be able to create your own. More on this later.

Water, I think, would be the biggest issue. Unless you could set up large-scale desalination, or collect enough rain water, you'd by definition not be self-sustained. Desalination of seawater is extremely energy-intensive, so now you've replaced your dependence on transporting water with transporting energy. I'm not sure about rain water, but at the very least this would limit the geographical areas you could live in to those with sufficient rain. I don't know exactly what scale the city would have to be to cover all these needs, but it would be large. If you intend to do anything but cover basic needs ( i.e. have businesses and homes and what have you ), you're looking at even larger requirements.

Energy is the next big issue. The site I found mentions wind, solar PV, and wave energy. I can see why. Solar PV has some very obvious limitations, in that they can only function when there's sufficient sunlight ( really, all the sources mentioned have some form of limitation based on weather conditions ). You also need space for it, which is a considerable limitation at sea - and you already need it for farming. You'd need quite a lot of it, too, if you're going to desalinate your own drinking water. Again, I really don't have the knowledge necessary to make the calculations, and I could be overestimating the energy needs versus potential energy production.

One thing I don't see mentioned on the site, which is going to be a huge deal in any community of sufficient size, is waste management. Using human waste as fertilizer is, from what I can gather, risky. Composting apparently helps, but it still should not be used to fertilize vegetable gardens - which is obviously what you want.

Then there's all kinds of scrap, excess salt water, and all other kinds of waste you need to get rid of. Short of just chucking it in the sea ( which would be a bad idea for reasons I think should be quite obvious ), you'd either need large-scale storage, or regular pickups. Which again goes against the idea of being self-sufficient.

Now, if you're not looking at being self-sufficient ... I suppose it could be possible. I think it'd be more practical as an extension of extant cities, than building new cities at sea. The technical challenges would be far greater than with a city on land, though, so it would be something to consider only in places with appropriate conditions and a real need for more space.

So, in summary: If you want to be even remotely self-sufficient, you need space, and people. If you want space and people, you have to scale up. Scaling up means the requirements grow. A properly self-sufficient city at sea would have to be of considerable size - and would be both technically and economically difficult to set up.

The free city of Christiania, in an abandoned quarter of army barracks near downtown Copenhagen, was much moreof a success story, sort of - and a haven of controversy (not least about the street called, tellingly, "Pusher Street" where you could, for many years, openly buy any dope you wanted). That one still exists today, more than forty years after the initial squatting, despite many pledges by Danish politicians to oust the folks living there.

You can still buy drugs very openly there. It's also a generally lovely and friendly place! If Danish authorities did evict people ( which no doubt they do, since the area is prime real estate ), I imagine the damage to Copenhagen's economy ( and reputation ) would be greater than the benefits. As someone with an interest in urban geography, and a frequent traveler to Denmark, I'd be really interested in seeing some analysis of the economic gains ( from tourism, and to local businesses ) generated by Christiania. I imagine it would be quite considerable.